Authentic stereoscopic slide cameras have not been manufactured for more than 30 years and those available are old-fashioned, mechanical units that have several operational limitations. These include dual built-in lens that are not changeable, mechanical camera controls, exclusion of built-in level indicators (level camera is essential for taking good 3D slides) and difficult focusing adjustments, particularly in a dark environment. Other important 3D camera shortcomings include limited availability, due to current non-manufacture, and relatively high slide development costs.
A quality, well designed 35 mm camera slide bar can be effectively utilized to overcome deficiencies noted above and to produce 3D slides. A wide variety of slide bars can be found in camera shops. All are designed to contain two 35 mm cameras mounted horizontally and fired simultaneously by a twin cable release. Each camera holds its own strobe light in the standard hot shoe mounting position.
The efficacy of these slide bars is uncertain since they have never been designed for optimum performance. For example, because of typical 35 mm camera body dimensions, the closest possible horizontal positioning of the two lens is approximately six inches on center. This distance exceeds the desired lens spacing of 23/4 inches found on stereoscopic cameras. Also, firing two cameras at exactly the same time is nearly impossible since the cable release is simply a mechanical pin with standard tapered threads. Synchronization is theoretically possible, but is very difficult to achieve. Unequal firing causes variable lighting in each slide that results in exposure and indiscriminate shadow problems.
Since the commercial slide bars found in camera shops have obvious shortcomings, there is a need for an improved slide bar which can be utilized to accurately take a pair of slides using a single camera.